The present invention relates to an energy regulation system for an electrical power supply bus, in particular of the type used on board a satellite.
The network to be supplied with power on board a satellite, comprising the payload and the service platform of the satellite itself, is supplied with power from the following two energy sources, via a power supply bus:
a solar generator (using solar energy recovered by solar panels of the satellite), which converts light energy into electrical energy, and generally comprises a plurality of cells, and
an electrical energy storage unit comprising one or more batteries for storing a portion of the electrical energy from the solar generator and converting it into electrochemical energy that is available in the form of electrical energy during eclipses or consumption peaks.
As the person skilled in the art is well aware, the supply buses used on board satellites operate at a predetermined regulated voltage, generally 50 V or 100 V. This regulation optimizes the electrical and mass performance of the electrical equipment of the satellite and of the energy resources.
The document FR-2 785 103 describes one prior art energy regulation system for an electrical power supply bus.
Its basic principle is to regulate the power supply bus voltage distributed to the network by means of a shunt section between each cell of the solar generator and the network and a control system which distributes a control signal simultaneously to all the cells. Also, in accordance with the basic principle of the prior art system, the battery voltage is regulated by a series section delivering a charging current to the battery and connecting each cell of the solar energy generator to the latter.
In the prior art, the two sections of each cell (i.e. the section regulating the power supply bus voltage and the section regulating battery charging) cannot operate simultaneously and the system is controlled by logic which prevents simultaneous operation.
Bus voltage regulation as a function of the control voltage has priority. Thus the shunt sections are either open circuit (when energy is transferred to the network) or closed circuit (when energy is not used and is therefore lost).
The prior art system gives rise to a number of problems.
First of all, it cannot effect fine regulation of the charging of the battery in accordance with standard battery charging methods, in other words it cannot effect some of the charging at a constant current and further charging (the end of charging) at a constant voltage, i.e. with varying current.
It also relies on the onboard computer of the satellite to choose which cells control the battery charging regulation system and in particular simultaneous operation of the two sections of each cell. As the computer is itself supplied with power by the power supply bus, a system of this kind is not autonomous and cannot be truly reliable.
An object of the present invention is therefore to provide an energy regulation system for an electrical power supply bus that can operate autonomously on board a satellite, in particular without relying on the onboard computer of the satellite, and which optimizes energy use on board the satellite to enable battery charging and bus voltage to be regulated finely.
To this end, the present invention proposes an electrical energy regulator system for a power supply bus connected to a load network using said electrical energy, said system including:
an electrical energy storage unit,
a solar generator comprising a plurality of cells,
for each of said cells, means for regulating the power supply voltage of said bus adapted to impose on said cell one of the following three operating states:
a first state in which current from said cell supplies power to said bus,
a second state in which current from said cell supplies power to said storage unit, and
a third state in which said cell is shunted,
said cells being divided by said bus voltage regulator means into:
a first group in which at least one of said cells supplies power to said bus and one of said cells referred to as a bus voltage regulator cell is assigned to regulation of the voltage of said bus and to this end is in its first state only when maintaining a nominal bus voltage requires a top-up of current from said cell, and
a second group in which at least one of said cells is either in a second state or in a third state, as a function of a required charging current of said storage unit, the number of cells in the second state being a function of the required charging current,
wherein each of said cells further includes means for regulating the charging of said storage unit which assign at least one of said cells of said second group to supplying power to said storage unit and one of said cells, referred to as a storage unit charging regulator cell, to regulation of the voltage of said storage unit, to which end said storage unit charging voltage regulator cell is in its second state only when maintaining a nominal charging voltage of the storage unit requires a top-up of current from said cell.
The invention makes it possible to apply fine regulation not only of the voltage delivered to the load network but also to charging of the storage unit, without it being necessary to use the onboard computer of the satellite, which makes the regulation system of the invention autonomous and reliable.
The invention is based on using a second cell assigned to the regulation function, in addition to that assigned to fine regulation of the bus voltage, and dedicated means for regulating the storage unit charging voltage.
Also, because it can be substituted for complex, costly and bulky electronic battery chargers, the system of the invention is light in weight and therefore inexpensive to use on board a satellite, an application in which each additional gram represents a significant additional cost.
The bus voltage regulator means and the storage unit charging regulator means are advantageously independent of each other and, if the two regulation functions converge toward assigning a single cell to regulation of the voltage of the bus and to regulation of charging of the storage unit, priority is given to bus voltage regulation. This ensures a regulated supply to the network whatever happens.
In a preferred embodiment, the bus voltage regulator means compare, in each cell, an average error in the nominal voltage of the bus and a reference value for the average error, the reference value being constant in each cell and increasing from one cell to the next, and the lowest value being that of the bus voltage regulator cell. This improves the avoidance of convergence of the two regulation functions mentioned above.
In this case, to reduce further the risk of convergence, regulation of the bus voltage starts with the cells having the highest reference value for the average nominal bus voltage error.
In another advantageous embodiment, the means for regulating charging of the storage unit compare, in each cell, an average error in the nominal charging voltage of the storage unit and a reference value for the average error, the reference value being constant within each cell and increasing from one cell to the next, and the highest value being that of the storage unit charging regulator cell.
This further reduces the risks of convergence of the two regulation functions.
In this case, to reduce still further the risk of convergence, regulation of charging of the storage unit starts with the cells having the lowest reference value for the average error in the nominal storage unit charging voltage.
The bus voltage regulator means can include a shunt switch in each cell connected in parallel with the cell.
Similarly, the storage unit charging regulator means can include a series switch in each cell for coupling the storage unit to the bus.